I have a whine coming from my engine bay that rises and falls with RPM, driving or stopped in neutral. Seems to be worst when the engine is cold/freshly started in the AM.

Obviously the first thing to check is anything attached to the serpentine belt, I assumed it was the alternator but it was not. Water pump was done with timing belt and idler/tensioner in August of last year so my assumption is it isn't any of that stuff. Presumably it is either the power steering pump or the A/C compressor, but I don't have any other indicators of impending failure for those parts (no whine when turning, power steering oil looks fine, A/C still blows cold, etc.).

Is there anything else that I should check? Could it be turbo bearings on the fritz? It sounds a bit like the noise your transfer case/differential makes when you first change the oil, but the sound doesn't change whether I'm moving or stopped.

 

the idler pulley can go bad. I believe I replaced mine last yeat

 

Have you started it with serpentine belt removed? Only run it for a few minutes since water pump will be disconnected. That eliminates all accessories from making noise. Next inspect intake side of turbo for damage or endplay.

 

The idler pulley was just replaced. Can't completely rule it out as the source of the noise as sometimes parts are bad out of the box but it is a pretty low pitched whine. I guess more like a whirr than a whine.

Haven't tried starting it without the belt but it would be tricky as the noise is very quiet at idle and only becomes apparent at about 3k rpm. I definitely should pull the intake and check the turbine wheel though, that's a good idea.

 

You can rev it to 3k on a cold engine just don't do it very long. Think about how long it takes for you heater to work. Coolant is still there just not in circulation, like every startup when your thermostat hasn't opened. A few minutes and then shut it down.